WO 93/16663 discloses a hip joint prosthesis comprising an attachment part for a ball unit which is designed to be anchored in the neck of a human femur (collum femoris). The attachment part comprises a part for carrying a ball or caput intended to be attached to the collum after performing a resection of the head of the collum. The attachment part also comprises a fixture member comprising two main parts, a first part which is to extend through a bore hole from the collum towards the outer side of the femur and a second part intended to fit into a cylindrical cavity cut into the cancellous bone of the collum. A hip joint prosthesis of this kind is illustrated in FIG. 1 of the accompanying drawings. Further examples of prior art hip joint prostheses are disclosed in WO 93/01769 and WO 89/11837.
In order to obtain a strong anchorage of the prosthesis, as discussed in general terms in WO 93/16663, the fixture member is preferably brought into engagement with the inside of the cortical bone in the collum as shown in FIG. 1, since such a contact with the cortical bone will reduce the risk of mechanical loosening of the prosthesis fixture member. In order to achieve this engagement, the sectioning or cutting plane P along which the head is to be removed must make an accurately determined cutting angle .alpha..sub.c with the main axis (A--A) of the femur. The specific value of this cutting angle for a patient is normally determined in advance from radiographs of the femur.
Furthermore, it is also essential that said cutting plane is selected at an accurately determined cutting level L.sub.c in relation to the proximal end of the collum head to be removed, in order that the patient should not limp. This cutting level can also be determined in advance from radiographs of the femur.
It is therefore an object of the invention to make it possible to perform a resection of the head of the femoral collum with high precision along a cutting plane at such a predetermined cutting angle and cutting level.
It is also an object of the invention to make it possible to perform such high-precision cutting in a quick and reliable manner.
A specific object of the invention is to provide a cutting guide instrument by means of which both the cutting angle and the cutting level can be determined in a reliable and accurate manner, and which can be used for guiding a cutting blade or the equivalent along the cutting plane thus established.